this week I've tried to convert one of my existing projects into a library project, and use this library in my app project. I basically followed all the steps in Google's description, and everything looks good in Eclipse: The compiler is happy, no errors.

The thing is: An .apk file is generated, which is missing all classes from the library project! Everything else is there, resources and the R file from both projects - but not the classes from the library.

After my research in the last days I only found one thing that looks weird (apart from the ClassNotFoundException when trying to run the app), which is the console output when starting the app in the emulator:

However, I seem to have found a work-around: The source directory of the library project needs to be added as a linked source into the app project. I would have a assumed the Android Plugin does this, but for it works for me.

I am confused on what you mean by library project. a "library" in java is a collection of classes that can be reused and is imported into the build path of the particular project.... I think I am misunderstanding your terminology.

I had the same problem and here is a solution. Assume x is android project which uses y-lib android library project. In Eclipse go to x->properties->Android. If in Library box you can see a row with y-lib then remove it ("Remove" button) and add y-lib once again ("Add..." button). It will restore in classpath of x project with paths like y-lib_src_main_java (which you might have removed - like it was in my case)